Yes, a reptile do not urinate like a mammal. The white tip on their dung is in fact the uric acid that they excrete, this is a paste not a liquid.

The water released is not urine, though it is a form of self defence triggered by a stressful situation (Not very effective in my opinion.).

Like Pilane said, it is in fact their water supply which is held in a sac, since they are not that mobile and getting water can at times be a problem. And yes, this is the reason why you should not pick them up, it can lead to them releasing the water supply and in the end having dehydration problems and even dying.